Method and apparatus for measuring tightness of vessels



Sept. 2, 1952 R. B. JACOBS METHOD AND APPARATUS FOR MEASURING TIGHTNESS OF VESSELS Filed June 14, 1946 F? B. Jacabs P tented Sept. '2, 1952 METHOD AND APPARATUS FOR MEASURING TIGHITNE SS OF VESSELS Robert B. Jacobs, Rochester, N. Y., assignor, by

mesne assignments,

America as represented by Atomic Energy Commission the United States of the United States Application June 14, 1946, Serial No. 676,813

The present invention relates to a method and apparatus for measuring tightness of vessels and is more particularly directed to a-method and apparatus for more accurately measuring the rate of in-leakage in closedvessels.

It is a primary object of the present invention to provide an improved method and apparatus for measuring vessel tightness'or rate of in-leakage more accurately and in much shorter time than methods heretofore in use.

The method most commonly used to measure vessel tightness is known as the pressure buildup method and may be briefly described in connection with the following apparatus and in the following manner. Y

The apparatus comprises a vacuum pump connected to the vessel under test through a vacuum line, a valve in the line adjacent the pump, and a vacuum gauge such as the McLeodtype of gauge provided in the line between the valve and the vessel. To determine if there is .any leakage in the vessel and if there is any leakage, the amount thereof, the vacuum pump is operated with the valve open until the vessel is substantially completely evacuated. If the reading on the gauge does not show a substantially complete vacuum in the vessel, a leakage is present in the vessel. The next step is to close the valve and take a reading on the gauge. Further readings are taken at definite time intervals and from these readings the amount of in-leakage can be computed. It is readily apparent therefore, that if the leak is very small, and the vessel large, along period of time is necessary to take the necessary number of readings to compute the amount of in-leakage in the vessel.

The present method and apparatus makes possible a substantially quantitative measure of ves sel tightness or rate of in-leakage more accurately and in much shorter time'than the conventional pressure build-up method.

Other objects and advantages of the present invention will be apparent to those skilled in this art from the following description and accompanying drawing in which is shown a diagrammatlc illustration of a form 'of apparatus for carrying the present invention into effect.

' Referring to the drawing, reference numeral indicates the vessel under test, and numeral ll indicates a gas-tight hood enclosing the vessel conduit I2 is connected to the vessel and extends through the hood. An analyzer i3 is provided in a part of the conduit outside the hood that quantitatively measures the concentration of helium or other gaseous medium under test. A vacuum 4 Claims. (G1. '73-'40) flowing through the line l2. A calibrated reference leak M is connected to the vacuum line within the'ho-od and a valve '15 i interposed between the calibrated reference leak and the main portion of the vacuum line. A leak is a device for introducing a minute constant flow of a gas into an evacuated system. See A Variable Capillary Gas Leak, Reviewgof Scientific Instruments 6, 26 (1935), and Ni-er et al., United States Letters Patent No. 2,422,921. Reference numeral I6 in-.- di'cates an inlet for introducing helium or other suitable gaseous material into the hood. The unknown leak in the vessel under test may be indicated by numeral 1. A suction pump (not shown) is provided inthe line f2 above the analyzer 1 3 and is adapted to maintain a constant suction on vacuum line l2 while the test is being made.

The method of carrying out tion may be described as follows:

The vacuum pump (not shown) is operated until the vessel is substantially evacuated. Thereafter with the valve leading to the calibrated leak It in an open position, helium or any other gaseous medium is forced into the hood through an inlet l6 until its concentration therein is sufficient to give a predetermined reading on the analyser l3. This reading designated as Reading (1) is proportional to the total in-leakage consisting of (11) Unknown vessel leakage.

(b) Known leakage from the calibrated leak.

The valve l5 leading to the calibrated leak is then closed and a second reading taken designated as Reading (2). This reading is proportional to the unknown leakage alone. From these two readings the following equation may be derived? the present inven- Unknown leakage= Reading (2) Reading (1) Reading (2) This equation gives the unknown leakage in terms of the two readings referred to above and the value of the calibrated leak. Knowledge of the helium concentration in the hood during the test is not necessary, the only requirement is that this concentration remain substantially constant during the time that the readings are taken. Normally this requires from five to ten minutes. Well constructed hood-s show practically no decrease in helium concentration for longer periods.

The present invention has been described as applied to closed vessels, but it will be obvious that it is equally applicable to any closed system in X Calibrated leakage first and second measurements to determine the amount of vessel leakage.

3. An apparatus for determining vessel leakage which comprises a gas-tight hood surround ing the vessel under test, an inlet in the hood for the outlet and an analyzer in the vacuum line outside the hood for measuring the concentration of a designated gas passing through the line.

4. An apparatus for determining vessel leakage which comprises a gas-tight hood surrounding the vessel under test, an inlet in the hood for admitting gas therein, a vacuum line connected to said vessel, a calibrated reference leak connected to said vacuum valve in the line between the reference leak and measuring the concentration of helium passing through the line.

' ROBERT B. JACOBS.

. REFERENCES; CYITED The following references are of record in the file of this patent? UNITED STATES PATENTS Number Name 7 Date 1,933,791 Crouch Nov. 7, 1933 2,255,921 Fear 1- Sept. 16, 1941 2,387,786 Washburn Oct. 30,1945 2,422,921 Nier et a1 June 24, 1947 2,486,199 Nier Oct. 25 1949 7 OTHER REFERENCES Benedict et al., Engineering Developments in the Gaseous Diffusion Process, National Nuclear Energy Series, I '-16 pages 54e56. McGraw-Hill, New York. I 

